The invention relates to the making of plastic screen panels, and particularly to the making of abrasion-resistant, urethane surfaced screen panels which have substantial utility in the mining industry. The invention is an improvement upon the apparatus described in Benson et al U.S. Pat. No. 4,295,918, said patent being assigned to a common assignee and its subjct matter is incorporated by reference herein. The screen panel per se is described in copending application Ser. No. 301,546 filed Sept. 14, 1981, now U.S. Pat. No. 4,374,169, which is also assigned to a common assignee and which is also incorporated by reference herein.
The aforesaid Benson et al U.S. Pat. No. 4,295,918 discloses an apparatus for producing flat screen panels from profiled screen surface wires and transverse support rods. The wires and rods each have an extruded urethane surface which permits them to be fusion-welded to each other. The patented apparatus produces an excellent screen, but is very labor intensive in that each of the many profiled screen wires which form the screen surface must be individually loaded in a specific orientation into one of a plurality of closely spaced annular grooves. The grooves are formed in one of a pair of cooperating feed rolls, one of which is driven. The grooves serve to maintain the wires in parallel alignment as they are pushed to and through the welding station. At the welding station, the wires must also be initially positioned in grooves in a positioning or anvil roll which backs them up as a support rod is brought into pressure contact with them after the rod and wires have been heated by a heater bar. The time required to thread all the surface profile wires would not be too significant if the wire were to be supplied in a large reel to each groove. However, since the screen would typically be formed in a 42-inch width, and thus might have 260 or more wires, it is generally preferred to provide the wire in relatively short cut lengths of perhaps 20 feet. Such short lengths cause the threading time to become a substantial proportion of the overall screen manufacturing time. Furthermore, since both one of the feed rolls and the positioning or anvil roll must each be grooved, it is necessary to have different sets of rolls for every wire dimension and slot spacing which is to be produced.